Conventionally, for example, an automobile, a motorcycle, etc. includes a suspension for rockably coupling a wheel and a vehicle body together through an arm, a link, a rod, or the like. The suspension prevents impact and vibration of the wheel from being transmitted to the vehicle body by a damper provided with a spring structure. For example, in a suspension spring (spring structure) disclosed in JP 10-26166 A, two compression coil springs having the same winding direction are arranged in series, and end portions of the compression coil springs, which face to each other, are threadably fixed to and overlap each other. Further, the suspension spring is placed between a body-side tube supported on the vehicle body and an axle-side tube for supporting an axle. Further, the suspension spring is provided with a spring constant adjuster capable of changing an overlapping length of the compression coil springs.